Bob Mendelson sits at the front of the class at the Wellbridge Athletic Club in St. Louis. As the pedals start spinning, music from every era of his 90 years on earth plays over the speakers: legendary Broadway composer Cole Porter, recordings from the Stanford University marching band, and even Top 100 tunes.

The 90-year-old St. Louis native discovered spin classes 20 years ago at a now-shuttered health club he used to go to. There was a dark room filled with bikes that everyone kept going into. One day, he decided to join them. “It took me awhile to get used to the moves,” he says. “At the beginning, it was just work. I didn’t start off with a natural spinning talent.”

Still, he kept going. And soon after starting, some friends from the club approached him. They wanted the now-retired professor at the front of the class.

“A couple of the people there said, ‘You know a little bit about music,’ and ‘You’ve taught, so why don’t you teach spinning?’” Mendelson says. “So I got certified, and when that club closed, some of my friends went over to Wellbridge. They mentioned my name to the people who are running the show, and they wanted to meet me, and that’s it. That was six years ago.”

Mendelson took his years as a urban planning professor at Southern Illinois University at Edwardsville and adapted what he learned there to the studio. That’s why he does more than just play music and shepherd his classes through workouts: He takes them on destination rides—journeys from his life.

Using his knowledge of urban planning, he takes class through history lessons about the landscapes of some of his favorite places: Boston, where he was stationed as an officer in the Coast Guard during the Korean War; Pittsburgh, where a dear friend lives, as well as through San Francisco, Chicago, Miami, and, of course, his hometown of St. Louis.

I don’t spend time saying your head’s too low, your body is this, your body is that. The great athletes I know aren’t dictated by form. They’re great athletes because of their spirit.

Similar to a lesson plan, each ride begins with a drawing, where Mendelson maps out the sections of the specific city he’d like to incorporate. He then divides the journey—both around the city and down memory lane—into five segments.

“Each segment is a type of topography, and then I work very hard to have four or five songs that fit that [landscape],” he says.

Then his creations come to life in the studio. Take St. Louis for example. One of the rides hosted “there” is called “Eastern European Immigrants, 1880-2018,” where he tracks his family’s journey from Latvia to Missouri. Proud of his Jewish heritage, he features music written or performed by people of Jewish ancestry for that ride.

“I started out with the dances from West Side Story and Hava Nagila,” he says. “Then I did Paula Abdul and Lady Gaga and Drake and contemporary young singers. I loved it!”

For six years, Mendelson has enjoyed the community he has fostered at the athletic club. Fitness classes often have a propensity for becoming individualistic endeavor; it’s all too common for workout enthusiasts to spend an hour in the darkness with their heads down and their heart rate up.

In contrast, Mendelson speaks excitedly about all of his students, like the who told him that her grandfather went to his same high school. Or 1984 Olympic gold medal cyclist Mark Gorski, a friend of his son, who was in class the other day. “He was terrific and he wanted to come back, so I gave him a pass,” Mendelson says.

These experiences speak to the inclusive environment that the nonagenarian’s classes radiate. His teaching philosophy emphasizes a rider’s tenacity over perfect spin posture.

“I don’t spend time saying your head’s too low, your body is this, your body is that,” he says. “The great athletes I know aren’t dictated by form. They’re great athletes because of their spirit.”

But the rides aren’t just a study in geography. They double as a lesson in the power of the human spirit. Mendelson works out for 2.5 hours each day and teaches at least one spin session a week.

And don’t be fooled by his upbeat attitude or his age. That just masks how challenging the classes can be. At an age where most people have slowed down, Mendelson encourages his riders up rolling hills and down steep terrain. When things get tough—both in class and out—he’ll remind students that, “the big events come to us. We don’t create them. What we have control over is how we face them.”

Mendelson celebrated his milestone birthday in Boston two months ago, and he has no plans to retire from spin any time soon. He’s learned that you have to take life as it comes to you, and he gains satisfaction from facing the challenges head-on. “Life is work,” he says. “When you feel terrible or you feel like staying in bed, you get up and keep going forward.”